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Author Topic: Working with Titanium  (Read 59751 times)
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wobblywalrus
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« Reply #15 on: July 15, 2015, 11:57:33 PM »

Some of the newer Triumph use titanium valves.  There must be a way to get Ti to resist ignition.  The combustion chamber is a very hot place.

Looking down on the lathe from a bird's eye view, the bit holder centerline axis should be 90 degrees to the rotational centerline of the part with insert tooling, as shown in the first photo.  It should not be at an angle like in the second photo.

Looking down the rotational axis of the part, the top of the bit holder should be horizontal and at the same elevation as the rotational centerline as shown in the third photo.  The typical tool holder used for HSS steel tools, as shown in the fourth photo, is not suitable for insert tooling.

These are general rules and there are exceptions, like cutting tapers.   


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wobblywalrus
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« Reply #16 on: July 17, 2015, 12:40:18 AM »

Corrosion is a big issue with salt flat racing.  The corrosion resistance of non-ferrous alloys appeals, and metals of choice become titanium, stainless steels, the aluminums, brass, etc.  Positive results with initial efforts convince me of the value of the carbide insert.  A moderate investment in specialized tooling is justified.

Holders that position the tool level are hard to find for old lathes.  The 1/4 by 1/4 size holders for mine are especially scarce. The straight one pictured is hand made and it came with the lathe.  The offset holders are also hand made and they are new and from India.  They are available from Sam A. Mesher and the catalog entry is shown. 


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WhizzbangK.C.
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« Reply #17 on: July 17, 2015, 08:58:03 AM »

I'll tell you Bo, the best investment I made for my lathe (1936 vintage 10 inch Craftsman, flat ways and plain bearing headstock) was a quick change tool post with several holders. Worth it's weight in gold as far as I'm concerned. I held onto my lantern tool post for a while, but after not using it for almost 10 years I gave it away to a friend who got a lathe with no tool holder at all.
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« Reply #18 on: July 17, 2015, 08:06:53 PM »

Ed, cost was the only issue.  The modern tool post setup is better than the lantern.

The world of carbide inserts is intimidatingly complex.  I drove up to Mesher's in Portland and asked them all sorts of questions.  They gave me a handful of year old catalogs and said the Dorian ones explain what I need to know in an understandable format.  This is the one I will be referring to.  It is worth it to download it and to print it out.  www.doriantool.com/wp-content/uploads/dorian_tool_TurningTools_CarbideInserts.pdf     
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wobblywalrus
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« Reply #19 on: July 17, 2015, 08:11:39 PM »

I forgot the underscore after inserts.  www.doriantool.com/wp-content/uploads/dorian_tool_TurningTools_CarbideInserts_.pdf
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wobblywalrus
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« Reply #20 on: July 17, 2015, 08:48:40 PM »

The American National Standards Institute (ANSI) designations will be used here.  The tool holders shown earlier on this thread use CCMT 21.51 inserts.  Refer to Pages 54 and 55 of the Dorian catalog.

The first "C" is the bit shape.  It is an 80 degree diamond.  This cannot be changed without using a different tool holder.

The second "C" is a 7 degree positive rake.  The tool holder is made for this bit rake.   

The "M" is the tolerance.  It is plus or minus 0.005 inches for bit thickness.  Bits with different tolerances can be used in the holder.

The "T" is the bit type.  This means:  Hole.  1 sided chip breaker, 40 degree-60 degree ISO countersink.  A "W" insert can also be used in the tool holder.  It is similar to the "T" except it has no chip breaker.

The "2" is the bit size.  It is 1/4 inch.  This cannot be changed without switching to a different tool holder.

The 1.5 is the bit thickness.  It is 3/16 of an inch.  This is the size that fits the tool holder.

The "1" is the radius of the insert tips.  it is 1/64 inch.  This can be varied with use of the same tool holder.

An insert with a chip breaker has this designation where the underscored can be changed.  CC_T21.5_
An insert without a chip breaker has this designation.  CC_W21.5_

This insert geometry, clearance angle, size, type, and thickness is well suited for small belt driven lathes. 

 
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wobblywalrus
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« Reply #21 on: July 20, 2015, 12:22:17 AM »

The catalog has a section on various metals with troubles and cures.  A fuzzy copy of the Titanium section is shown. There is a lot of info in this publication.  It is much more than just a listing of what they sell.

The preceding post listed two bit sizes.  There are only two entries in the catalog for them.  One is for bits without a chip breaker groove CCGW-21.51-KEU.  These are best for cast iron and I will use them to skim the brake disks on my truck.  Uncoated DKU10HT is best in the wet condition.  My lathe has no coolant and I work with dry conditions.  This coating is not optimal.  DUP35RT coating works with wet/dry conditions.  It is best for roughing with cuts .008 to .157 deep.  The belt on my lathe will slip when I try these deep cuts.  This is not the best choice.  DUP15VT is best in dry conditions with .002 to .098 inch deep cuts.  This matches the lathe capability and it is the best choice.  I will order a few.

The third posted page shows bit CCGT-21.51 with UEU chip breaker groove.  It works best for almost all materials.  The DUP15VT coating is best for shallow cuts in the dry condition.  This is what I am using now.

These posts show a method to use these tools.  It can be adapted to use on many metals with other brands of inserts.       

 


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wobblywalrus
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« Reply #22 on: July 21, 2015, 12:39:30 AM »

Titanium is hard to almost impossible to thread with a die using normal methods.  The die seizes in place and is very hard to turn.  Sometimes the threaded end twists off of the part and it is stuck in the die.  Special methods are needed to make male threads.

The shaft is turned to the diameter shown in the first photo.  A die is used to cut threads.  Note how the outside diameter increases when it is threaded as shown in the second pix.   The die cuts and extrudes threads.  This jams up the die if the rod to be threaded is turned to the major diameter.  Jamming is less of a problem if the shaft is turned undersize before it is threaded.

My formula is shaft diameter = major diameter - (2 x 20% of thread depth) where thread depth (metric threads) = (0.5 x thread pitch) / tan 30 degrees

For example, the major diameter is 10 mm for this rod with 10 mm x 1.25 mm threads.  Thread depth is (0.5 x 1.25 / 0.57753 = 1.083 mm.  Undersize shaft diameter is 10 - (2 x .2 x 1.083) = 9.566 mm = 0.377 inches.  The shaft is turned to this diameter before threading with the die.   


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rouse
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« Reply #23 on: July 21, 2015, 09:14:52 AM »

Your best bet for threading Ti would be to single point thread it on the lathe.

Your right that die threading is not an easy thing to do, almost not possible to do right with good results, as you material will twist with the torque of the die and the rebound will lockup on the die, and there your are, stuck.

Set the parts up in the lathe and single point your threads.

By the way; if you use a Ti nut or any Ti female thread with these parts you will need to coat these threads with something to prevent galling, or they well "weld together" as soon as they are torqued.

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wobblywalrus
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« Reply #24 on: July 22, 2015, 01:20:56 AM »

The lathe works great for making American threads.  The bike is metric.

An adjustable die is used to make the first pass.  The die is loosely clamped in the holder so it can expand as needed.  Anti-seize is used as a cutting lubricant.  The first pass partially cuts the threads.  More lubricant is applied and a non-adjustable die is used for the second pass.  Most of the time this is the finish pass.  The titanium compresses in the die when it is cut.  Sometimes a third pass with a very sharp die is needed to cut the threads to the proper size.

Rouse give good advice about using unlubricated titanium to titanium connections.  They can friction weld together.

 

 


* 2015 Tit 031.jpg (104.57 KB, 800x600 - viewed 147 times.)
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Rex Schimmer
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« Reply #25 on: July 26, 2015, 03:12:30 PM »

When I was working at Standard Tool and Die in LA we did quite a lot of Ti machining and as previously stated machine rigidity is a big requirement. One of the things that we did for doing the rough cuts when milling Ti was to use liquid nitrogen for the cutting fluid. Makes Ti cut like aluminum. Fun to watch the end mill snap the micro second that the liquid nitrogen stopped!

Rex 
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« Reply #26 on: July 31, 2015, 12:35:14 AM »

That is amazing.  I wonder how they figured out that it would work?

The formula I use for metric tap drill size is:  tap drill diameter in mm = thread outside diameter in mm - (1.08254 x TE x thread pitch in mm) where TE = 0.65 for 65% thread engagement or 0.75 for 75% thread engagement

Usually I start with a tap drill for 75% engagement, and if it is hard to turn, the hole is enlarged to the size for 65% thread engagement.  Anti-seize is used as a thread lubricant.

Taps made for ti are essential.  Two entries in the Sam Mesher catalog are shown.  The taps I use are selected from these lists.  They are used for ti only, and nothing else.  They are easy to turn and cut nice threads.     


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« Reply #27 on: September 29, 2015, 02:54:11 AM »

There is an easier formula for cutting metric threads:

outer diameter minus thread pitch is the diameter of the bore to drill:

Metric 8mm has 1,25mm pitch so its: 8 - 1,25 = 6,75mm (6,8mm) Drill
Metric 8mm FINE has 1mm pitch so its: 8 - 1 = 7mm  Drill

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« Reply #28 on: October 17, 2015, 05:57:55 AM »

You're spot on Weal. cheers
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wobblywalrus
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« Reply #29 on: October 17, 2015, 11:38:45 PM »

The thing I am trying to show is that the titanium piece is turned to a slightly smaller diameter than is customary before the die is used to cut male threads, and the hole is drilled slightly bigger than normal before it is tapped.  This makes the ti easier to thread with normal taps and dies.  Otherwise, the metal is very difficult to work with and it is easy to break the tap or have other big problems.  Quite often I do not need to do this if special taps and dies are used that are made to cut titanium.
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